Minimally invasive surgery (MIS) provides surgical techniques for operating on a patient through small incisions using a camera and elongate surgical instruments introduced to an internal surgical site, often through trocar sleeves or cannulas. The surgical site often comprises a body cavity, such as the patient's abdomen. The body cavity may optionally be distended using a clear fluid such as an insufflation gas. In traditional minimally invasive surgery, the surgeon manipulates the tissues using end effectors of the elongate surgical instruments by actuating the instrument's handles while viewing the surgical site on a video monitor.
A common form of minimally invasive surgery is endoscopy. Laparoscopy is a type of endoscopy for performing minimally invasive inspection and surgery inside the abdominal cavity. In standard laparoscopic surgery, a patient's abdomen is insufflated with gas, and cannula sleeves are passed through small (generally ½ inch or less) incisions to provide entry ports for laparoscopic surgical instruments. The laparoscopic surgical instruments generally include a laparoscope (for viewing the surgical field) and working tools.
The working tools are similar to those used in conventional (open) surgery, except that the working end or end effector of each tool is separated from its handle by a tool shaft. As used herein, the term “end effector” means the actual working part of the surgical instrument and can include clamps, graspers, scissors, staplers, image capture lenses, and needle holders, for example. To perform surgical procedures, the surgeon passes these working tools or instruments through the cannula sleeves to an internal surgical site and manipulates them from outside the abdomen. The surgeon monitors the procedure by means of a monitor that displays an image of the surgical site taken from the laparoscope. Similar endoscopic techniques are employed in other types of surgeries such as arthroscopy, retroperitoneoscopy, pelviscopy, nephroscopy, cystoscopy, cisternoscopy, sinoscopy, hysteroscopy, urethroscopy, and the like.
Endoscopy may be performed with robotically controlled working tools. Robotic control may provide an improved control interface to the surgeon. Robotically controlled working tools may be driven by servo mechanisms, such as servo motors, that are coupled to the working tool by mechanical cables. Each servo mechanism may be coupled to a cable by a capstan that draws in and pays out the cable wound around the capstan. The cable may be routed to and from the capstan by one or more pulleys. The cable may rotate a driver that is coupled to the robotically controlled working tool to drive and control movement of the tool. As space in the surgical field where robotically controlled working tools are being used is at a premium, it is desirable to have a compact mechanism to drive and control the robotically controlled working tools.
In a typical cable drive system for a robotically controlled working tool, a cable is guided by a pulley and wound onto a capstan that is rigidly fixed to a shaft. The capstan being rigidly fixed to the shaft it can only be rotated with the shaft. As a result, the point at which the cable comes onto the capstan moves along the length of the capstan as the capstan rotates. If the capstan is close to the pulley guiding the cable, a large angle can be created in the cable at a take off point at the capstan. If this angle is too large, the cable may wear excessively, incur physical damage to its cable strands, run off the take off pulley, or run out of a groove in the capstan. By increasing a distance between the capstan and the pulley, the angle at the take off point may be reduced and be acceptable. However, this makes the cable drive system less compact. It is desirable to minimize the angle in the cable at the take off point of the capstan while at the same time providing a compact mechanism to drive and control movement of a robotically controlled working tool.
It will be appreciated that all the drawings of Figures provide for herein are for illustrative purposes only and do not necessarily reflect the actual shape, size, or dimensions of the elements being illustrated.